Filter cloth and process of preparing same



' I chemical agents and materials.

Patented Nov. 7, 1950 FILTER cLo'rn raocass mar-same SAME 'Ottomar H. Van Norden, New York, N. Y.,'ls-

signer to Metakloth Company,

Lodi, N. 1., a

corporation of New Jersey No Drawing. Application August :0, 1948, Serial No. 45,433. In Canada September 5, 1m

1 Claims. (cl. 210-403) The present invention relates to a process for preparing a filter cloth specifically for use in the filtration of alkaline aqueous liquids and to the cloth as prepared in accordance with the present invention.

The problem of filtration of highly alkaline liquids is a serious one in practice, particularly when means such as the usual filter presses are to be used. This is because most cloths such as are normally employed in presses or for covering the leaves of leaf filters are made of cotton, and this material is in effect destroyed chemically by reaction with the highly alkaline aqueous liquids to be filtered, if the cloth is used untreated. Consequently it is customary to treat the cloth. but treating processes heretofore employed had as their purpose th complete preparation of the cloth prior to its use as a filter and exposure to the alkaline aqueous liquids to be filtered, and in general involved immersing the cloth to be treated in a series of baths containing diiferent The cloth was thereby prepared in finality for filtering any of a variety of aqueous liquids. Such prior processes required repeated handling and removal of excess liquids between baths. In accordance with the,

present invention the cloth is not completely prepared in its eventual operative condition prior" The cloth is brought to this eventual to use. operative condition only upon being subjected to its actual intended use in filtering alkaline aqueous liquids. Moreover, the amount of handling heretofore employed for impregnating the various chemical agents and materials into the cloth is reduced in accordance with the present lnvezi tion.

I have found that by impregnating cloth with a soluble salt of any of certain metals at the same time as or prior to the impregnation with some emulsified form of a petroleum product and/or mineral wax, superior results are obtained. The provision of such a process is one of the objects of the present invention. A further object of the present invention is to provide a process as aforesaid, wherein the impregnation step may be effected using but a single bath, thus simplifying the apparatus required for carrying out the process and resulting in operating economies in' the process itself, as well as in th attaining of superior results,- as compared with those attainableby prior processes.

Other and more detailed objects of the present invention will appear from the following detailed specification and will be pointed out in the appended claims.

. 2, Inasmuch asthe process of the present invention may becarried out by the use of conventional apparatus, which will immediately suggest itself to those skilled in the art from the description of the process, its illustration in drawings is unnecessary.

Briefly, the invention consists in impregnating a cloth of suitable character in a bath of a desired composition as hereinafter set forth, then expressing or otherwise mechanically removing from the cloth any liquid of the impregnating bath in excess of that required to saturate the cloth, then drying the cloth in a conventional manner.

From a mechanical point of view, the impregnation may be conducted by passing the cloth a desired number of times over rolls, some of which are immersed beneath the surface of the desired impregnating bath contained in any suitable container or tank. The excess liquid may be removed from the cloth by conventional means, such as calender .or squeeze rolls. If the cloth is in relatively small pieces, they may be placed in a centrifugal extractor.

The drying of the cloth may be eliected in any suitabl manner, for example by passing a continuous web thereof serially over heated drums or rolls'ordry cans or by festooning or by placing in dry boxes.

The bath used for impregnating the cloth is preferably a single bath in accordance with the present invention, so that only one single impregnation is required. This bath has two principal constituents; first, a water-soluble salt of a metal which is selected from the group consisting of cerium. zirconium and lanthanum salts; and second, an emulsion of a suitable mineral wax. such for example as a paraflin wax or some other mineral wax, preferably amorphous in character, which may be found desirable and operative. This emulsion must in practice be stabilized by the presence in the, bath of a suitable emulsifying agent its-hereinafter set forth.

Optionally present ingredients, which are preferably used in accordance with the preferred form of the present invention, include a buffer composition. which is used to-stabilize the pH of the bath, so as to maintain the-pH slightly on the alkaline side of neutral. i. e. from 7 to about 9 in value. Any suitable soluble composition, such as one or more-soluble salts, may be used for this purpose. It may also be desired to use an additional material having an alkaline reaction in aqueous solution, such for example as soda ash, to assist the buffer salt in its operation and to amount in practice will depend upon the physical characteristics of the cloth, such as weight, absorptiveness, etc. Salts of certain metals, as cerium, zirconium and lanthanum are contemplated for use in accordance with .the present invention. It is preferred to use such salts which are reasonably commercially available and which form soluble metal salts so that they 'can be de-v posited in the cloth in this way, yet which will react with alkali to form a gelatinous hydroxide which is relatively insoluble in water. All these factors are desired and considered substantially essential characteristics.

The particular salts used in accordance with I the present invention is usually and preferably the chlorides, although any other soluble salts of cerium, zirconium and lanthanum which are available and which. will not interfere with other portions of theprocess may be used as equivalents. Such other salts will include the nitrates, acetates, sulfates and possibly others. The essential feature, from the point of view of the pres: ent invention is that thesalt used be freely soluble in water up to any concentration which may be desired for use.

The wax emulsion used in this case should be one which has a continuous aqueousphase. The

; wax used is preferably an amorphous mineral wax, which will be unaffected by chemical reaction 'with any of the other materials of the bath and/or with any materials which the finally treated cloth may be used for filtering. Such waxes are almost never water-soluble, so that they mustbe dispersed in the aqueous bath as an emulsion. For this purposeany suitable emulsifying agent, including many of the so-calledwetting agents may be employed. Triethanolamine hasbeen found quite satisfactory for this purpose. The emulsifying or wetting agent is usually present in an amount merely sufficient to stabilize the emulsion, which in the case of many wetting agents is about 1% of the emulsion as originally prepared in readiness to be added to the remainder of the bath, this being the normal way in which the bath is made up.

It is desired to have the bath substantially on the alkaline side of neutral. For this purpose a chemical agent which is water-soluble and which hasa distinctly alkaline reaction in aqueous solution may be added to the bath. Such an agent is soda ash. As a substitute for soda ash a rela tively smaller amount of a strong alkali, such as sodium hydroxide, could be used with equivalent results. Other equivalents will occur to those skilled in the art.

It is usually preferred to control the pH of the solution and to stabilize it at some particular value, normally'on the alkaline side of neutral. Thus the pH in accordance with the above invention should be above 7 and preferably not over about 9. This result may be effected by the use I of any conventional buflfer salt, such for example 'afssodium acetate.

. An example, of an impregnating bath which is preferred in accordance with the present invention is as follows:

' When'the data given above is calculated, it will I be found that the liquid present totals 52 gallons, .which is increased slightly by the addition of the solid soda ash'and sodium acetate. Based upon this, there is present in the solution, wax in a concentration of about 1.2 pounds per gallon, which figure may also be about 1.3 if desired, and cerium chloride in a concentration of about 1.15 pounds per gallon.

As to the method of preparing the solution, it is usual separately to prepare the wax emulsion and the cerium chloride solution. The latter has a specific gravity-when prepared in the proportion suggested above in the particular example given of 29.92 Baum.

Followin the impregnation and drying of the cloth, the cloth is ready for cutting into desired shapes and sizes for installation in a conventional filtering apparatus, such as a filter press.

When a strongly'alkaline aqueous solution is filteredihrough the cloth in the normal use of the press, the alkali in the solution in the filtrate reacts with the cerium salt with which the cloth is impregnated as aforesaid, so as to precipitate through the fibers of the cloth itself a gelatinous and substantially water-insoluble precipitate of cerium hydroxide. This protects the filaments and fibers of the textile material of the cloth from subsequent damage by chemical attack by the solutes in the filtrate. The same reaction occurs when any of the zirconium and lanthanum salts are used.

It has been found in practice that when the desired final end products, i. e. the hydroxide of the metal used, is created or formed by chemical reaction in the fibers of the cloth after the cloth has been installed as a filter, the results from the use of this cloth then and thereafter are superior to those which may be attained from an attempt, to prepare the insoluble metal compound in the cloth as a preliminary treatment step. The reason for this is not clearly understood and hence no theory attempting to explain it will be set forth herein, the present invention being limited to the preparation of filter clot-h which is to be used'in this manner so as to attain these most desirable results.

It has further been found that when the solution being filtered is not only highly alkaline but more or less saline as well, equivalent desirable results are attained. It is necessary, however, for -the best results that the solution'to be filtered the bath of an emulsifying agent, and

The particular impregnating hath given above may be satisfactorily used with many types of commercial filter cloth, although the proportions of certain of the ingredients may be changed somewhat for optimum results, if cloth of some other character is used. For this reason I do not wish to be limited to the particular concentrations herein given for use with all kinds and weights of filter cloth.

While there is disclosed herein but a relatively few examples and equivalents, I do not wish to be limited except by the scope of the appended claims, which are to be construed validly as broadly as the state of the prior art permits.

What is claimed is: 1. The process of treating filter cloth to prepare it for use in the filtration Of alkaline aqueous liquids, comprising impregnating a cloth in a single bath comprising an aqueous solution of a water-soluble salt of a metal selected from the group consisting of cerium, zirconium and lanthanum, and an emulsion of a mineral wax having an aqueous continuous phase, said emulsion being stabilized by the presence in the bath of an emulsifying agent, while maintaining the pH of said solution between 7 and about 9, and thereafter drying the cloth.

2. The process of treating filter cloth to prepare it foruse in the filtration of alkaline aqueous liquids, comprising impregnating a cloth in a single bath comprising an aqueous solution of a water-soluble salt of cerium, a water-soluble butler composition for controlling the pH of the bath to a value between 7 and about 9, and an emulsion of an amorphous mineral wax having an aqueous continuous phase, said emulsion being stabilized by the presence in the bath of an emulsifying agent, and thereafter drying the cloth.

3. The process of treating filter cloth to prepare it for use in the filtrationof alkaline aqueous liquids, comprising impregnating a cloth in a single bath comprising an aqueous solution of cerium chloride, a water-soluble builer salt in a concentration adequate to control the pH of the solution to a selected value within the range of 7 to about 9. and an emulsion of an amorphousmineral wax having an aqueous contin .ious phase,

aqueous continuous phase, said emulsionbeing o0 stabilized .by the presence in the bath of tri- 6 ethanolamine as anemulsifying agent, and thereafter drying the cloth.

5. The process of treating filter cloth to prepare it for use in the filtration of alkaline aqueous liquids, comprising impregnating a cloth in a single bath comprising the following ingredients in the proportions listed:

Water, 30 gallons Soda ash, 1 /2 lbs.

Cerium chloride (solution), 56 lbs. cerium chloride made up to 15 gallons of solution Sodiumacetate (buffer), 2 /4 lbs.

Emulsion of amorphous mineral wax, 63 lbs. of

wax made up to 7 gallons in an aqueous solution using about 1% triethanolamine as an emulsifying agent thoroughly impregnating and saturating the cloth in the bath as thus prepared, mechanically removing from the cloth liquid of the bath in excess of that required for saturation, and drying the cloth.

6. As an article of manufacture, a filter cloth for use in the filtration of strongly alkaline aqueous liquids, comprising a cloth of absorbent textile material, impregnated throughout the fibers thereof with cerium chloride, which is present in the cloth in amounts such as will remain when the cloth is impregnated with an aqueous solution having a pH between 7 and about 9 and having a concentration of cerium chloride of about 1.15 pounds per gallon, and the excess liquid of the bath above that required to saturate the cloth mechanically removed therefrom, leaving the remainder of the dissolved cerium chloride in the cloth upon drying, said cerium chloride being partly sealed into the clothby a mineral wax, said cloth as thus prepared being capable oi reacting in its subsequent use with the aqueous alkaline liquid to be filtered therethrough, so as to precipitate cerium hydroxide in the cloth.

7-. A filter cloth in accordance with claim 6, wherein the amount of said wax in the cloth upon the completion of its preparation is substantially that which would be left in the cloth' treated as I aforesaid by impregnating it with an aqueous liquid containing a wax emulsion in a concentration of about 1.3 pounds of wax per gallon.

OT'IOMAR' H. VAN NORDEN'.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,222,100 Hanson Apr. 10, 1917 2,228,320 Magruder et al Jan. 14, 1941 2,291,080

Hoiferbert July 28, 1942 

1. THE PROCESS OF TREATING FILTER CLOTH TO PREPARE IT FOR USE IN THE FILTRATION OF ALKALINE AQUEOUS LIQUIDS, COMPRISING IMPREGNATING A CLOTH IN A SINGLE BATH COMPRISING AN AQUEOUS SOLUTION OF A WATER-SOLUBLE SALT OF AMETAL SELECTED FROM THE GROUP CONSISTING OF CERIUM, ZIRCONIUM AND LANTHANIUM, AND AN EMULSION OF A MINERAL WAX HAVING AN AQUEOUS CONTINUOUS PHASE, SAID EMULSION BEING STABILIZED BY THE PRESENCE IN THE BATH OF AN EMULSIFYING AGENT, WHILE MAINTAINING THE PH OF SAID SOLUTION BETWEEN 7 AND ABOUT 9, AND THEREAFTER DRYING THE CLOTH. 